Python Unindent Does Not Match Any Outer Indentation Level

How to resolve the error indentationError: unindent does not match any outer indentation level?

I don’t know why I am seeing this error please help me here is my code:

import sys 

def factorial(x): # Return factorial 

res = 1 

for j in range (1,x): 

res = res * j 

print "factorial is ",res

return res